The Research Of Genetic Evolutionary Algorithm On Structural Optimization

The subject of optimum structures is currently undergoing something of a boom. Engineers have realized the importance of the gains that can be made by a rational approach to design, which quantifies a principle of minimum cost. Topology optimization methods for continuum structures have achieved significant progress in the last two decades. These techniques have increasingly been used in aeronautical, mechanical and automotive industries in which the weight reduction of structures is very important. However, the potential of structural optimization techniques has not been realized by civil engineering industry and most works are designed by trial and error based on individual engineering experiences. As officers of the Ministry of Construction estimated, civil engineering industry is promising in China and the total of 30 billions m2 buildings will be constructed until 2020. As the relative lack of resources in our country the development and application of optimal theory is very important task for construction industry. On this background this thesis focuses on the structural topology optimization.Topology optimization methods include evolutionary structural optimization (ESO), homogenization, density function, genetic algorithm (GA), et al, among which evolutionary structural optimization attained more attention for its simple concepts and easy programming. But ESO often came under some suspicious remarks for no guarantee of optimum structures. GA is excellent in optimization by using Darwinian's theory of survival of the fittest though having no definite mathematic background. The time-consuming characteristics of GA in engineering limited its application to truss structures instead of plane or space structures. However, a new method deal with topology optimization of plane structures was proposed in this dissertation on the basis of ESO and GA. The new algorithm is named genetic evolutionary structural optimization (GESO) which starts from an original design field consist of all potential optimum structures and computed sensitivity numbers as done in ESO, selected and deleted elements from a ground structure by genetic operation such as mutation and crossover. Combination of the genetic operations and the process of ESO decrease the possibility of improper element being deleted. Compared with the results acquired by ESO, the topologies obtained by the new GESO are more exact while the time consumed is lesser than that of GA. It is shown in succeeding studies that the acquired optimums are insensitive to the value of parameters, so the robustness of the new method is proved.Another innovative work in the dissertation is connecting GESO with Michell theory. The Michell theory of least-weight trusses for one load condition and a stress constraint was established in a milestone contribution by Michell (1904, Australia). Michell theory plays an important role in structural topology optimization. In general, Michell truss is a kind of framework with continuous distributions of members. It is often called"truss-like continuum"which is difficult to be deduced by mathematics analysis. In the dissertation the numerical studies of the new method use the classical Michell trusses for verifying their results. On the other hand, with the numerical calculations by GESO new"Michell type"structures are presented. Two or more pin-point supported plane structures under different loadings attained more attentions in the studies of discovering their optimal principle of topology. A large number of numerical experiments gained two main kinds of optimums for pin-point plane structures that is the structure composed of straight lines and circles and the structure made up of"Michell cantilever"and cycloids. These conclusions are of significant importance to structural concept design.GESO can be conveniently applied to reinforcement layout optimization in reinforced concrete structure. Reinforced concrete is a composite material and the nonlinear behavior of reinforced concrete is characterized by the cracking of concrete and the yielding of steel reinforcement. The key problem for which solutions are obtained are whether the stiffness of reinforcing steel and the nonlinear behavior of reinforced concrete can be considered in the finite element model. Three schemes were then designed for the question. The answer is that the stiffness of reinforcing steel and the nonlinear behavior of reinforced concrete cannot be taken into account in the finite element model. After extensive cracking of concrete, the loads applied to a reinforced concrete member are mainly carried by the concrete struts and steel reinforcement. The failure of a reinforced concrete member is mainly caused by the breakdown of the load transfer mechanism, rather by that the tensile stress attains the tensile strength of concrete. The design task is to develop an appropriate strut-and-tie model for the structural concrete member in order to reinforce it. Simple supported beams with different span-to-depth ratios, deep beams, corbels and beam-column connections are discussed for acquiring optimal reinforcement layout which can be used in engineering structures.